I wouldn't bring just water on anything longer than a 15 mile ride, but I don't use anything fancy, just Gatorade. There's one flavor at my local grocery that's clear so that's what I buy. I did look at trying EFS powder, which is like liquid PowerBar, but it's not sold anywhere around me.

Oh and for PowerBars I like the Harvest, Recovery and Triple Threat (any of them with chocolate). The Performance bars are much more compact for carrying with you and don't fall apart when you eat them on a ride.